In a conventional magnetic storage system, a thin film magnetic head includes a read/write element mounted on a slider. The magnetic head is coupled to a rotary actuator magnet and a voice coil assembly by a suspension and an actuator arm positioned over a surface of a spinning magnetic disk.
In operation, a lift force is generated by the aerodynamic interaction between the magnetic head and the spinning magnetic disk. The lift force is opposed by equal and opposite spring forces applied by the suspension such that a predetermined flying height is maintained over a full radial stroke of the rotary actuator assembly above the surface of the spinning magnetic disk. The flying height is defined as the spacing between the surface of the spinning magnetic disk and the lowest point of the slider assembly.
One objective of the design of magnetic read/write heads is to obtain a very small flying height between the read/write element and the disk surface. By maintaining a flying height close to the disk, it is possible to record short wavelength or high frequency signals, thereby achieving high density and high storage data recording capacity.
The slider design incorporates an air bearing surface to control the aerodynamic interaction between the magnetic head and the spinning magnetic disk thereunder. Air bearing surface (ABS) sliders used in disk drives typically have a leading edge and a trailing edge. A thin film read/write element is formed at the trailing edge of the slider.
Generally, the sliders have tapered portions at the leading edge and longitudinal side rails that extend from the tapers to the trailing edge. The tapers may be shaped and of such length as to provide fast pressure buildup during takeoff of the slider from a rest position to a flying height relative to the disk with controlled pitch. The dimensions and shapes of the tapers and side rails are instrumental in determining the flying characteristics of the head. The side rail design determines the pressure generated at the ABS of the slider. In effect, the pressure distribution on the ABS contributes to the flying characteristics of the slider that include flying height, pitch, and roll of the read/write head relative to the rotating magnetic disk.
In a conventional magnetic media application, a magnetic recording disk includes a landing zone, which is defined as an annulus area of a width of about 0.2 inch located at the inner radius of the magnetic disk. The landing zone is a textured area and its sole function is to provide a surface upon which the slider comes to rest in between track seeks during a read/write operation. The surface of the landing zone typically is optimized to have a certain degree of roughness so as to prevent stiction between the slider and the disk and yet enable a fast take-off of the slider.
As the trend toward high capacity storage applications continues, smooth media applications have emerged to supplant conventional media applications with increasing acceptance due to a principal advantage of smooth media disks in offering a higher data storage capacity than conventional media disks. This advantage is afforded by the absence of the landing zone, which is reclaimed for increasing the data storage area of a magnetic disk. Hence, a smooth media disk is characterized by a finely polished surface in its entirety from the outer radius to the inner radius of the disk without a landing zone.
Accompanied with the emergence of smooth media disks, the current trend in the magnetic storage technology has also been to push the slider design toward a near zero flying height in order to reduce the magnetic spacing, thereby increasing the data recording capacity. This type of slider design is typically referred to as proximity or contact recording, which employs a contact pad concept, wherein a small pad is etched around the pole tip region. Furthermore, to attain high linear or areal density, such a slider design may include a giant magnetoresistive (GMR) read/write sensor.
In proximity recording, the air bearing surface (ABS) is typically designed to have high a pitch stiffness that causes the contact pad in the trailing edge region of the ABS, to which the read/write sensor is physically attached, to remain in actual contact with the highest asperities on the smooth media disk surface during the initial phase of operation. Because of this contact action, surface wear of the slider as well as the media disk takes place during this process, which is also referred to as burnishing.
Since the contact point is localized at the contact pad region, the pads burnishes continuously. The burnishing process gradually decelerates and eventually stops when the contact pad no longer encounters any asperities on the smooth media disk surface, thereby achieving a steady state clearance. Thereupon, the goal of the proximity recording is realized as the slider attains a near zero flying height and thereby reduce the magnetic spacing. Hence, the success of the proximity recording head depends on understanding and controlling the wear evolution of slider-disk interface.
Because of the surface contact with the magnetic storage disk made by the trailing edge region of the ABS, the surfaces of the magnetic storage disk and the ABS of the conventional slider experience a continual erosion or wear, thereby resulting in material loss from both the magnetic storage disk and the ABS. This material loss forms debris in the vicinity of the pole tip region of the read/write sensor. As the debris accumulates, the ability of the proximity recording head to register binary data onto the magnetic storage disk suffers a significant degradation due to an increase in spacing between the pole tip and the surface of the magnetic storage disk. The head is no longer flying, but is supported by the contamination. In general, the severity of the wear is controlled within the specified design tolerances by optimizing the tribology of the ABS material. The maximum wear is proportional to the initial interference height of the slider-disk interface. If the wear were not properly controlled, the burnishing would eventually expose the GMR read/write sensor to the ambient. Because of its susceptibility to atmospheric corrosion, the GMR read/write sensor may fail to achieve its functionality and proximity recording performance when exposed to the drive environment.
To address this concern in the slider design of a proximity recording head, presently an exemplified tribological design incorporates a conventional diamond-like carbon (DLC) protective pad onto the trailing edge region of the ABS wherein the read/write sensor is mounted. The conventional DLC protective pad is generally formed by a two-layer material comprising of an outer DLC layer disposed above an underlying silicon (Si) seed layer. The outer DLC layer is usually derived from ethylene as a precursor, hence also referred to as E-DLC.
While the conventional two-layer DLC pad may have in theory provided a satisfactory resolution of the foregoing concern, in practice it does have a serious deficiency that likely renders the goal of proximity recording unattainable. This deficiency lies in the fact that due to manufacturing tolerances, there exists a small deviation in the design flying height of the slider, which herein is referred to as sigma. The flying height sigma translates into a distribution of interference height, resulting in some sliders exposing to larger interference heights than others. Consequently, this presents a number of challenging problems to the conventional DLC pad.
Because the E-DLC layer of the conventional DLC pad would experience a varying degree of burnishing due to the flying height sigma, the proximity recording heads employing the conventional DLC pads thus cannot in general achieve uniform steady state clearance or magnetic spacing, thereby leading to a varying performance of such proximity recording heads.
Moreover, the inability to cope with the distribution of flying height sigma also increases the risk of a potential excessive wear of the E-DLC layer of the conventional contact DLC pad when the slider is flying closer to the magnetic disk surface than the average flying height. In some instances, the wear of the conventional contact DLC pad is so extensive that allows the read/write sensor to be exposed to the corrosive environment in which the proximity recording head operates. Once exposed, the read/write sensor becomes oxidized or corroded quite rapidly, thereby resulting in damage to the proximity recording head and consequently causing catastrophic failure of the magnetic disk drive.
In light of unresolved concerns with the conventional DLC protective pad employed in proximity recording applications, it is realized that there is an unfulfilled need for an improved DLC pad design for proximity recording that addresses the problems associated with the flying height sigma variation of the sliders in the proximity recording heads. Preferably, the improved DLC pad design should be insensitive to the flying height sigma in a manner that would allow the burnishing to achieve uniform steady state clearance and magnetic spacing in spite of the variation in the flying height. More importantly, the improved DLC pad design should be able to provide a complete protection of the read/write sensor during burnishing by limiting the wear process. These preferences, therefore, establish a goal for proximity recording that would enable the current advancement in high capacity magnetic storage applications to continue to progress.